Sir Alex Ferguson has increased speculation that Manchester United may be about to make a bid for Borussia Dortmund's Robert Lewandowski by suggesting the striker's summer move to Bayern Munich may not be the done deal everyone imagines.

A long-term admirer of the Poland centre-forward, Ferguson said as recently as last week that he thought Lewandowski would end up at Bayern, the side he appears likely to face in the Champions League final after scoring all four goals in Dortmund's semi-final first leg victory against Real Madrid.

Bayern have already caused some ill‑feeling in Germany by announcing the capture of Dortmund's Mario Götze in the week of the semi finals, prompting Jürgen Klopp, Borussia's coach, to promise that Lewandowski will not make the same move. Ferguson appears to believe him and, though his assertion that Dortmund will let Lewandowski's contract run down appears somewhat fanciful, it may be that United will attempt to follow last summer's signing of Shinji Kagawa with an even bigger name from the same club.

"If the right player comes along you have to be prepared to make a move," Ferguson said. "I can find room for anybody here as long as they have the required quality. I am not sure Lewandowski will be sold to Bayern now. The Dortmund fans are not going to be happy and I don't think they will sell to their main rivals. I think they will either let his contract run out, or sell him somewhere else."

Ferguson watched Dortmund on Wednesday, possibly interested in midfield targets as well as Lewandowski, and saw nothing to shake the belief he has held since the start of the campaign that Klopp's side has what it takes to win the Champions League. "But for the referee [in United's defeat to Real Madrid] it would have been us facing Dortmund, and we would have had to do a good job, because they are a good side," he said. "Our target for next season is to do better in Europe, possibly by adding a player or two, but it will be interesting if this season's final is an all-German affair."

Ferguson noted Bayern's poor record against Borussia – they have not won any of the past five Bundesliga meetings, despite some cup successes – and added: "I have said all along that Dortmund have been prioritising the Champions League this season. They have an unbelievable record against Bayern, so despite what the German league table might say, if the two sides meet in the final it wouldn't be a gimme for Bayern."